While not restricted thereto, this invention finds direct application in simple, inexpensive off-line power supply circuits and in simple, inexpensive battery charging and forming circuits which are especially useful for forming and/or charging batteries used in portable battery-operated devices, including cordless devices, such as soldering pencils, shavers, cordless telephones, calculators, computers, television sets, radios, recorders, electric garden tools, cordless hand tools including woodworking and metalworking tools, and the like. The present invention also finds direct application in off-line power supplies and in battery charging and forming circuits useful in aircraft, automobiles and other mobile machines, as well as in battery formers and chargers such as those used at aircraft repair facilities, automobile service stations and the like, and in battery forming circuits, battery charging circuits and in off-line power supplies of general application.
The terms battery charging and battery charger as used herein include respectively battery recharging and battery recharger as well, in accordance with contemporary usage of these terms.
Battery-operated devices, such as hand tools, have considerable popularity because of the convenience afforded by these devices. Many devices of this type are customarily provided with a small D.C. electric drive motor which is energized by one or more rechargeable batteries incorporated within the tool housing and operatively associated with the electric drive motor. When the device is a television set, radio, recorder or the like, the rechargeable batteries supply D.C. power to the circuits therein either exclusively or alternatively, in instances in which an A.C. power cord and plug are provided. The elimination of a conventional electric cord or its alternative use increases the freedom with which the user of the cordless device can move about, thereby overcoming the inconveniences of clearing the power cord from obstacles with which it may otherwise become entangled and reducing the necessity of having electric wall outlets available at every place the device is to be used. It has become customary to provide cordless devices, such as cordless garden tools and woodworking tools with rechargeable batteries, thus avoiding the necessity of frequent battery replacements, and to reduce the cost of operation.
It is known from U.S. Pat. No. 3,943,423 to Philip A. Hoffman entitled "Battery Charging Circuit" and issued on Mar. 9, 1976 to provide a battery charging circuit which, when recharging batteries in a hand tool or the like, needs simply to be connected to a conventional, 117 volt 60 Hz. household outlet and to the battery cell or cells which are to be recharged. Other outlet voltage levels and/or supply frequencies can be used as well. The known charging circuit of the aforesaid U.S. Pat. No. 3,943,423 to Philip A. Hoffman, supra, comprises a variable resistance switch preferably realized in the form of a junction transistor and Darlington-connected other transistors operatively associated with a feedback circuit. This known circuit, which produces current pulses twice each rectified half wave, requires negative feedback and has, in addition to the transistors, resistors, two rectifying diodes and two capacitors, resulting in a circuit which, particularly because of the need for feedback circuitry, capacitors and a considerable number of passive components becomes relatively expensive to realize. No provision has been made to adjust the circuit, once constructed, for different capacity loads.
It is known from the further U.S. Pat. No. 3,970,912 issued on July 20, 1976 to Philip A. Hoffman and entitled "Battery Charging Circuit" to provide a battery charging circuit operatively arranged to produce, twice each rectified half wave, current pulses which are supplied to the battery or batteries to be recharged via the inductance of an electric motor, which forms part of a cordless hand tool or the like. This circuit, while not requiring capacitors to operate, does require negative feedback and an inductance which is a portion of a motor, that is the inductance of an electric motor in a powered hand tool or the like. No provision has been made to adjust the circuit, once constructed, for different capacity loads.
An apparatus is known from the U.S. Pat. No. 4,134,056 to Katsuo Fukui et al. entitled "Apparatus for Charging a Battery" and granted Jan. 9, 1979 for charging batteries which involves a circuit having a differential amplifier, one of its inputs being fed from a circuit point between a point from a series connected capacitor and a resistor, its other input being fed via a resistive voltage divider connected across a fixed D.C. source. The capacitor and resistor are used as a differentiating circuit.
A battery charger and power supply is known from U.S. Pat. No. 4,321,523 to Ronald O. Hammel entitled "Battery Charger and Power Supply Circuitry" and granted Mar. 23, 1982 which includes a rectifier, a voltage regulator, a SCR switch, the switch being controlled by a timing circuit which fires the SCR at a selected point intermediate to the beginning and end of each rectified half wave. An operational amplifier, responsive to a reference voltage and battery voltage, provides one of the two inputs to the trigger circuit, its other input being from the voltage regulator. While current feedback is not used, the circuitry must include an accurate timing circuit.
Another battery charging circuit is known from U.S. Pat. No. 3,310,724 to Dennis R. Grafham entitled, "Battery Charging Regulators" granted Mar. 31, 1967 which includes a first controlled SCR. A second SCR, arranged to respond to the battery voltage level, controls the first SCR which conducts during peak portions of each half wave until the battery is sufficiently charged. An additional rectifier and variable resistor provide a trickle charge path.
A battery charging circuit is known from U.S. Pat. No. 3,867,681 to Larry D. Bishop et al. entitled "Battery Charging Circuit" granted Feb. 18, 1975 which includes a current regulator and a switch, the switch being controlled by a logic circuit, including an AND gate and two OR gates. An operational amplifier, responsive to a reference voltage and a battery voltage, provides one of the inputs to one of the OR gates, as well as to a control input of a latch circuit, the output of which is supplied to the second OR gate. Each OR gate receives its second input from respective timers.
A considerable number of battery chargers, as well as off-line power supplies have been proposed and are known from the general prior art including U.S. Patents identified as follows:
______________________________________ Numbers Patentees Issue Date ______________________________________ 3,617,852 Phoenix Nov. 2, 1971 3,735,233 Ringle May 22, 1973 3,781,631 Nelson et. al. Dec. 25, 1973 3,876,921 Bigbee, III Apr. 8, 1975 3,919,617 Tippett et al. Nov. 11, 1975 4,013,934 Frye Mar. 22, 1977 4,019,111 Bennefeld Apr. 19, 1977 4,128,798 Takai Dec. 5, 1978 4,134,056 Fukai et al. Jan. 9, 1979 4,140,958 Groeschel Feb. 20, 1979 4,158,813 Ellis et al. Jun. 19, 1979 4,162,439 Schneider Jul. 24, 1979 4,186,335 Cahill Jan. 29, 1980 4,220,905 Quarton Sep. 2, 1980 4,266,178 Asakaw May 5, 1981 4,292,578 Steigerwald et al. Sep. 29, 1981 4,342,955 Gant Aug. 3, 1982 4,348,619 Ray et al. Sep. 7, 1982 4,458,195 Piteo Jul. 3, 1984. ______________________________________